The present invention relates a headlamp for motor vehicles. More particularly, it relates to a headlamp for motor vehicles which has a discharge lamp inserted into a reflector and surrounded by a glass envelope which is transparent in certain sections to light of specific wavelengths.
Such a headlamp is disclosed in EP-A1-0 237 647. This headlamp has a discharge lamp whose discharge vessel is surrounded a glass envelope made of hard glass. The discharge vessel is melt-sealed into the glass envelope so that these parts are combined to form one unit. The space between glass envelope and discharge vessel is evacuated. The glass envelope is provided in certain sections with a coating which is non-transparent and by means of which an asymmetrical light distribution required in dipped headlamps is achieved. By means of the glass envelope, the UV-A light portion and UV-B light portion of the light transmitted by the discharge lamp is blocked to a specific degree since, due to its properties, glass generally inhibits the passage of these portions. However, the UV-C light portion which is injurious to health and also destroys plastics is not blocked by a glass envelope consisting merely of customary glass. In addition, if the glass envelope is touched when the headlamp is damaged, for example after an accident, there is a risk of combustion. The reason is that the high temperatures prevailing in the discharge vessel are transmitted to the glass envelope and if the electrical terminals of the discharge lamp are touched there is a risk of lethal injury since the lamp is operated at a high voltage.